How to Deploy a Flask App to Heroku

Nov 27, 2016 10:20 · 504 words · 3 minute read Python Flask Heroku

The deploy tutorial on <Flask Web Development> has somehow been out-dated. Follow this blog and you will know the differences.

Sign up for Heroku

Visit Heroku website and create your own heroku account. Try not to forget your password immediately.

Install Heroku Toolbelt

Download Heroku toolbelt and install it as guided.


After installing heroku toolbelt properly, open your terminal.

$ heroku login
Enter your Heroku credentials.
Email: <your-email-address>
Password (typing will be hidden): <your-password>
Uploading ssh public key .../

Enter your email address and password, and you are logged in. Btw, the login command will automatically (create and) upload your SSH public key.

Create an app

$ heroku create <appname>
Creating <appname>... done, stack is cedar
http://<appname> |<appname>.git
Git remote heroku added

There’s little to talk about at this step. just try to think of a fascinating name for your own app, and it should always inlude only lower case letters. (Try not to and you’ll get an error just as I did.)

Now you have a domain and a remote git repository. Will use them later.

Config database

Now this is (seemingly?) the only different step from the tutorial in <Flask Web Development>.

$ heroku addons:add heroku-postgresql:hobby-dev
Creating heroku-postgresql:hobby-dev on ⬢ <appname>... free
Database has been created and is available
 ! This database is empty. If upgrading, you can transfer
 ! data from another database with pg:copy
Created postgresql-lively-71535 as DATABASE_URL
Use heroku addons:docs heroku-postgresql to view documentation

Now the environment variable DATABASE_URL has saved the URL for the database. And this is the end of configuring database :)

Set environment variables

Now you may tell me there are a few things you don’t want to put in your codes cause they are so important. So let’s save them in Heroku’s environment. And this is the usual format:

$ heroku config:set <ENV-VAR-NAME>=<value>

As for me I set:

$ heroku config:set <appname>_CONFIG=heroku
Setting <appname>_CONFIG and restarting ⬢ <appname>... done, v4
<appname>_CONFIG: heroku
$ heroku config:set MAIL_USERNAME=<mymailusername>
Setting MAIL_USERNAME and restarting ⬢ <appname>... done, v5
MAIL_USERNAME: <mymailusername>
heroku config:set MAIL_PASSWORD=<mymailpassword>
Setting MAIL_PASSWORD and restarting ⬢ <appname>... done, v6
MAIL_PASSWORD: <mymailpassword>

Run produce environment web server

Hekoru doesn’t provide a produce server, so we have to supply our own.

(venv) $ pip install gunicorn

Add requirements.txt

Just put all the requirements in your project’s root in a file named requirements.txt.

Add Procfile

Another file to add, at root, named Procfile, containing:

web: gunicorn manage:app

That’s it.

Now there’s one more part which I’m not gonna talk about in this blog since it depends on your code:

  • Use Flask-SSLify to initial safe HTTP

Please try to work through this (or read chapter 17.4.3 in <Flask Web Development>) before continuing.

Implement your deploy

$ git push heroku master
$ heroku run python deploy

Where deploy is a command declared in aiming to upgrade database.


# ...
def deploy():
    """Run deployment tasks."""
    from flask_migrate import upgrade

    # migrate database to latest revision
# ...
$ heroku restart

And you’re ready to go!